1. Field of the Invention
This invention relates to an electronic flash device for a photographic camera and, particularly, to an electronic flash device arranged to determine an aperture value through a preliminary flashing action and to set the light control level of a main flashing action in accordance with the aperture value. The term "light control level" as used herein for the purpose of this invention means a predetermined value of quantity of light received at which the main flashing action is to be stopped.
2. Description of the Prior Art
There have been proposed electronic flash devices of the kind arranged to determine an aperture value of a phototaking lens according to the quantity of a reflection light received as a result of a preliminary flashing action thereof and then to perform a main flashing action at a light control level corresponding to the aperture value. There has also been proposed a flash device in which a preliminary flashing action is performed when a shutter release button of the camera is depressed to the first stroke position thereof; then, it is confirmed whether an object to be photographed is located at a distance within a light control range, that is, whether the distance between the camera on which the flash device is mounted and the object to be photographed is within a light controllable range which is, for example from 0m to 8m if the guide number of the flash device is 16 and, if the aperture value designated by the flash device is F2.0, the confirmation is arranged to be made, for example, through a display of an aperture value then selected; and after this has been confirmed, a flash photographing operation is carried out by further depressing the shutter release button to a second stroke position thereof.
Generally, in the case of a flash device having a guide number 16, the designated aperture is in the following relation to the light control range:
______________________________________ Designated aperture: F 2.0 F 4.0 F 8.0 ______________________________________ Light control 0 m &lt; D &lt; 0 m &lt; D &lt; 0 m &lt; D &lt; range D: 8 m 4 m 2 m ______________________________________
With the above stated flash device used, therefore, the aperture of the phototaking lens is set at F2.0 when the preliminary flashing action is performed on an object located at a distance D which is 4m&lt;D&lt;8m. Then, the flash device is set at a light control level corresponding to this aperture value. Meanwhile, a display allows the photographer to confirm that the object is located within the light controllable distance range. Under this condition, when a flash photographing operation is performed by approaching the object, for example, to a point of 0m&lt;D&lt;4 m from the object, a proper exposure is obtainable if the lens is brighter than F2.0 and can be set at F2.0. However, if the lens is of a full aperture F-number of F4.0, for example, the aperture value of the lens gives an under-exposure by two steps because the light control level has been set at a value corresponding to F2.0. This presents a serious problem in cases where flash photographing must be carried out by moving a camera closer to or farther away from an object to be photographed by using various kinds of interchangeable lenses.